If you and your husband are basically negotiating aspects of your relationships that will directly affect your additional partners, it would be fair and respectful for them to have their own direct voice in those negotiations. It's their relationship, too.

While I see your point, that one couple should not negotiate boundaries for another couple, I disagree on this particular point. This is about whether a certain person is allowed to sleep in someone's home.

Your home needs to be a safe place. If you would feel put out or uncomfortable by having someone in your house, then that person's desire to be in your house is irrelevant. It's your house, not theirs.